This study addresses our current inability to determine whether renal artery lesions are hemodynamically significant. We hypothesize that patients with renal artery stenosis will have less increase in renal blood flow than normal subjects following a vasodilatory stimulus. We plan to attempt to induce renal vasodilation using dopamine and amino acids in normal subjects, hypertensive subjects, and patients with renal artery stenosis. Renal blood flow will be measured using Doppler ultrasonography, & para-amino hippuic acid.